Magnetic recording medium and manufacturing method of the same

ABSTRACT

A magnetic recording medium enabling excellent magnetic recording reproduction characteristics to be exhibited with the spacing loss reduced. The magnetic recording medium has a magnetic recording layer of a granular structure having nonmagnetic boundary portions between pillar-shaped magnetic particles on a nonmagnetic substrate, and an exchange coupling layer provided on the magnetic recording layer to add an action of exchange coupling the magnetic particles. Ion irradiation on the entire surface of the exchange coupling layer after layering the exchange coupling layer on the magnetic recording layer is performed

This is a Divisional of application Ser. No. 12/745,194 filed May 27,2010, claiming priority based on International Application No.PCT/JP2009/054395, filed on Mar. 9, 2009, which claims priority fromJapanese Patent Application No. 2008-067028 filed Mar. 17, 2008, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to magnetic recording media andmanufacturing method of the media and more particularly, to magneticrecording media in perpendicular magnetic recording type andmanufacturing method of the media.

BACKGROUND ART

In recent years, in magnetic recording apparatuses typified by a HDD(Hard Disk Drive), since the high recording resolution is obtained,perpendicular magnetic recording type have been put into practical usewhich are comprised of perpendicular two-layer media and single-polehead. Further, as measures for enhancing the in-plane recording density,techniques have been developed to make the magnetic layer bearingrecording finer. In the techniques, heat stability of magnetic particlesdeteriorates due to finer particles, and faced is the so-called thermalfluctuation problem such as deterioration and loss of recordedinformation. To solve the problem, it has been carried out to providethe magnetic fine-particle structure with increased heat stability usingan exchange-coupling type medium that magnetically couples magneticparticles to magnetically stabilize. For example, in CGC media, granularhaving a fine-particle structure is provided with an exchange couplinglayer, and mutually separated magnetic particles are exchange-coupledvia the exchange coupling layer (Patent Document 1).

-   Patent Document 1: U.S. Pat. No. 6,468,670

DISCLOSURE OF INVENTION

However, in order to strengthen the exchange coupling in theabove-mentioned structure, it is required to increase the thickness ofthe exchange coupling layer to some extent. When the thickness of theexchange coupling layer is thickened, the distance from the mainrecording layer bearing recording to a magnetic head is inevitablyincreased, and there is a problem that the so-called spacing loss isincreased.

The present invention was made in view of the aforementioned respect,and it is an object of the invention to provide a magnetic recordingmedium enabling excellent magnetic recording reproductioncharacteristics to be exhibited with the spacing loss reduced, and amanufacturing method of the medium.

A method of manufacturing a magnetic recording medium of the inventionis a method of manufacturing a magnetic recording medium formanufacturing a magnetic recording medium having a magnetic recordinglayer of a granular structure having nonmagnetic boundary portionsbetween pillar-shaped magnetic particles on a nonmagnetic substrate, andan exchange coupling layer provided on the magnetic recording layer toadd an action of exchange coupling the magnetic particles, and ischaracterized by having an ion irradiation step of performing ionirradiation on the entire surface of the exchange coupling layer afterlayering the exchange coupling layer on the magnetic recording layer.

A method of manufacturing a magnetic recording medium of the inventionis a method of manufacturing a magnetic recording medium formanufacturing a magnetic recording medium having a magnetic recordinglayer of a granular structure having nonmagnetic boundary portionsbetween pillar-shaped magnetic particles on a nonmagnetic substrate, andan exchange coupling layer provided on the magnetic recording layer toadd an action of exchange coupling the magnetic particles, and ischaracterized by having an ion irradiation step of performing ionirradiation on the entire surface of the exchange coupling layer so thatan amount of change in the ratio c/a of the c axis to the a axis in acrystal lattice of a metal having a hexagonal close-packed structurecontained in the exchange coupling layer is 10.21% or more.

According to these method, by ion irradiation, it is possible toeffectively control minute exchange coupling occurring between themagnetic recording layer having a fine structure hard to prepare and theexchange coupling layer, it is thus possible to perform with easewithout changing various characteristics as a magnetic recording medium,and the magnetic recording media can thereby be manufactured withoutreducing productivity.

In the method of manufacturing a magnetic recording medium of theinvention, it is preferable that the exchange coupling layer is a filmcontaining Pt and Co, and that the metal is Co.

In the method of manufacturing a magnetic recording medium of theinvention, it is preferable that the thickness of the exchange couplinglayer is 7 nm or less, and that a dose in the ion irradiation is in therange of 1×10¹³ to 1×10¹⁵ (ions/cm²).

In the method of manufacturing a magnetic recording medium of theinvention, it is preferable that in the ion irradiation step, ions areapplied from above a protective layer after layering the exchangecoupling layer on the magnetic recording layer and further forming theprotective layer on the exchange coupling layer.

A magnetic recording medium of the invention is a magnetic recordingmedium having a magnetic recording layer of a granular structure, wherepillar-shaped magnetic particles spatially have nonmagnetic boundaryportions therebetween, on a nonmagnetic substrate, and an exchangecoupling layer provided on the magnetic recording layer to add an actionof exchange coupling the magnetic particles, and is characterized inthat reversed magnetic domain nucleation magnetic field Hn is −2000Oe(×10³/4π A/m) or more, a ratio Hn/Hc of reversed magnetic domainnucleation magnetic field Hn to coercive force Hc is −0.5 or less, andthe thickness of the exchange coupling layer is 7 nm or less.

According to this configuration, by performing ion irradiation on theexchange coupling layer, although the film thickness is thin, it ispossible to exhibit high exchange coupling force. Therefore, withoutincreasing the spacing loss, it is possible to obtain excellent magneticrecording reproduction characteristics with the exchange coupling forceexerted.

In the magnetic recording medium of the invention, the exchange couplinglayer preferably contains Pt, Co and Cr.

The magnetic recording medium of the invention is a magnetic recordingmedium having a magnetic recording layer of a granular structure, wherepillar-shaped magnetic particles spatially have nonmagnetic boundaryportions therebetween, on a nonmagnetic substrate, and an exchangecoupling layer provided on the magnetic recording layer to add an actionof exchange coupling the magnetic particles, has reversed magneticdomain nucleation magnetic field Hn of −2000Oe (×10³/4π A/m) or more, aratio Hn/Hc of reversed magnetic domain nucleation magnetic field Hn tocoercive force Hc of −0.5 or less, and a film thickness of the exchangecoupling layer of 7 nm or less, and is capable of reducing the spacingloss and exhibiting excellent magnetic recording reproductioncharacteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a magnetic recordingmedium according to an Embodiment of the invention;

FIG. 2 is a graph illustrating the relationship between an amount ofchange in lattice constant and a dose of ion irradiation;

FIG. 3 is a graph illustrating the relationship between an amount of C/Achange and the dose of ion irradiation;

FIG. 4 is a diagram illustrating the relationships between an exchangecoupling layer thickness, and Hc and Hn;

FIG. 5 is a graph illustrating the relationships between the exchangecoupling layer thickness, and Hn/Hc and the gradient a of themagnetization curve;

FIG. 6 is a graph illustrating the relationship between Hn/Hc and thedose of ion irradiation; and

FIG. 7 is a graph illustrating the recording density dependence ofstandardized output obtained from output voltage.

BEST MODE FOR CARRYING OUT THE INVENTION

An Embodiment of the invention will specifically be described below withreference to accompanying drawings.

FIG. 1 is a cross-sectional view showing a schematic configuration of amagnetic recording medium according to an Embodiment of the invention.This magnetic recording medium is a magnetic recording medium used inperpendicular magnetic recording reproduction type.

The magnetic recording medium 100 as shown in FIG. 1 is comprised of adisk base 10, adhesive layer 12, first soft magnetic layer 14 a, spacerlayer 14 b, second soft magnetic layer 14 c, orientation control layer16, first underlayer 18 a, second underlayer 18 b, magnetic recordinglayer 22, auxiliary recording layer 24, medium protective layer 26 andlubricating layer 28, where each layer is stacked in this order. Inaddition, the first soft magnetic layer 14 a, spacer layer 14 b andsecond soft magnetic layer 14 c constitute a soft magnetic layer 14. Thefirst underlayer 18 a and second underlayer 18 b constitute anunderlayer 18.

As the disk base 10, for example, it is possible to use glasssubstrates, aluminum substrates, silicon substrates, plastic substrates,etc. When glass substrates are used as the disk base 10, for example,amorphous aluminosilicate glass is formed into a disk shape by directpress to prepare glass disks, and the glass disks are subjected tolapping, polishing and chemical strength successively to prepare thebase.

The adhesive layer 12 is a layer to enhance adhesion with the disk base10, and is capable of preventing the soft magnetic layer 14 from peelingoff. As the adhesive layer 12, for example, it is possible to use CrTifilms, etc.

As the first soft magnetic layer 14 a and second soft magnetic layer 14c of the soft magnetic layer 14, for example, it is possible to useFeCoTaZr films, etc. Examples of the spacer layer 14 b include Ru films.The first soft magnetic layer 14 a and second soft magnetic layer 14 cundergo antiferro-magnetic exchange coupling (AFC), the magnetizationdirection of the soft magnetic layer 14 can thereby be aligned along themagnetic path (magnetic circuit) with high accuracy, componentsperpendicular to the magnetization direction are extremely reduced, andit is possible to decrease noise occurring from the soft magnetic layer14.

The orientation control layer 16 protects the soft magnetic layer 14,while promoting orientation of crystal particles of the underlayer 18.As materials for the orientation control layer 16, it is possible to usea material selecting from Ni, Cu, Pt, Pd, Zr, Hf and Nb. Further, withthe metals as a main component, it is possible to use alloys containingone or more additive elements of Ti, V, Ta, Cr, Mo and W. For example,NiW, CuW and CuCr are suitable.

Materials constituting the underlayer 18 have an hcp structure, and arecapable of growing crystals of the hcp structure of materialsconstituting the magnetic recording layer 22 as a granular structure.Accordingly, as the crystal orientation of the underlayer 18 is higher,it is possible to enhance the orientation of the magnetic recordinglayer 22. Among the materials for the underlayer 18 are RuCr and RuCo,as well as Ru. Ru has an hcp structure, and enables the magneticrecording layer with Co as a main component to be oriented withexcellence.

In this Embodiment, the underlayer 18 is comprised of a Ru film of atwo-layer structure. In forming the second underlayer 18 b on the upperside, the gas pressure of Ar is made higher than in forming the firstunderlayer 18 a on the lower side. When the gas pressure is increased,since the free migration length of sputtered plasma ion is reduced, thedeposition rate is decreased, and the crystal orientation is improved.Further, by increasing the pressure, the size of the crystal lattice isdecreased. Since the size of the crystal lattice of Ru is larger thanthe crystal lattice of Co, decreasing the crystal lattice of Ruapproaches the crystal lattice of Co, and it is possible to furtherenhance the crystal orientation of the granular layer of Co.

The magnetic recording layer 22 is a magnetic layer of a one-layergranular structure. Examples of materials for the magnetic recordinglayer 22 are CoCrPt—Cr₂O₃, CoCrPt—SiO₂, and CoCrPt—TiO₂. These materialsmay contain a plurality of oxides.

The exchange coupling layer 24 is a thin film (auxiliary recordinglayer) showing high perpendicular magnetic anisotropy and highsaturation magnetization Ms (saturation magnetization Ms higher thanthat in the granular magnetic layer 22) on the granular magnetic layer22, and exchange-couples magnetic particles in the magnetic recordinglayer. The exchange coupling layer 24 is intended to improve reversedmagnetic domain nucleation magnetic field Hn, resistance to thermalfluctuations, and overwrite characteristics. As the exchange couplinglayer 24, for example, it is possible to use CoCrPt and CoCrPtB films.In the magnetic recording medium with such a configuration, exchangecoupling is provided in between the magnetic recording layer and theexchange coupling layer.

The layers of from the adhesive layer 12 to exchange coupling layer 24are deposited successively on the disk base 10 by a DC magnetronsputtering method in an atmosphere of Ar using a vacuumed depositionapparatus. With consideration given to productivity, it is preferable toform the layers and films by inline type deposition.

The medium protective layer 26 is a protective layer to protect themagnetic recording layer from shock of a magnetic head. Examples ofmaterials constituting the medium protective layer 26 are Cr, Cr alloys,carbon, zirconium, and silica. Generally, carbon deposited by a CVDmethod improves the film hardness as compared with the film deposited bya sputtering method, and is capable of protecting the perpendicularrecording layer more effectively against shock from the magnetic head.

As the lubricating layer 28, for example, perfluoro polyether (PEPE)that is a liquid lubricant is diluted with a solvent such as Freon, isapplied onto the medium surface by a dipping method, spin coating methodor spray method, and undergoes heating processing when necessary, andthe layer 28 is formed.

Described next is the exchange coupling layer of the magnetic recordingmedium according to the invention.

In the magnetic recording medium according to the invention, it ispreferable that the exchange coupling layer 24 contains a metal having ahexagonal close-packed structure, and that an amount of change in theratio c/a of the c axis to the a axis in a crystal lattice of the metalranges from 10.21% to 10.81%.

In the hexagonal close-packed structure, a state, where an amount ofchange in the ratio c/a of the c axis to the a axis ranges from 10.21%(+0.2% or more or −0.2% or less) to 10.81% (+0.8% or more or −0.8% orless), is a state where the hexagonal close-packed structure becomesdistorted. In other words, this state distorts the hexagonalclose-packed structure, increases (extends) the a-axis lattice spacing,and decreases (shrinks) the c-axis lattice spacing. To thus distort thehexagonal close-packed structure, ion irradiation is performed on theentire surface of the exchange coupling layer 24. By the applied ions,it is possible to narrow the c-axis lattice spacing, and widen thea-axis lattice spacing in the hexagonal close-packed structure. Inaddition, an amount of change in each of the c axis and/or the axis is10.11% or more (+0.1% or more or −0.1% or less), and preferably, 10.21%or more (+0.2% or more or −0.2% or less).

The inventors of the invention measured X-ray diffraction of theexchange coupling layer irradiated with Ar+ ions and examined on whetherthe hexagonal close-packed structure becomes distorted by ionirradiation. Herein, a CoCrPtB film containing Pt and Co was used as theexchange coupling layer, and the crystal lattice of Co was examined. Theresults are shown in FIGS. 2 and 3. As can be seen from FIG. 2, as thedose in ion irradiation increases, the a-axis lattice spacing isincreased, and the c-axis lattice spacing is decreased. Further, as canbe seen from FIG. 3, as the dose in ion irradiation increases, an amountof change in c/a is increased. In this way, it was confirmed that thehexagonal close-packed structure becomes distorted by ion irradiation.

The conditions of ion irradiation to thus distort the hexagonalclose-packed structure can be determined as appropriate in considerationof the film thickness of the exchange coupling layer 24. For example,when the thickness of the exchange coupling layer 24 ranges from 3 nm to7 nm, the dose in ion irradiation preferably ranges from 1×10¹³ to5×10¹⁴ (ions/cm²).

The film thickness is thinned in the exchange coupling layer with thehexagonal close-packed structure thus distorted. Described next is theexchange coupling force of the exchange coupling layer with the filmthickness thus thinned. When the film thickness is changed in theexchange coupling layer 24, the coercive force (Hc) and reversedmagnetic domain nucleation magnetic field (Hn) change. As the exchangecoupling layer 24 is thicker, Hc decreases and the absolute value of Hnincreases (the value is negative, and therefore, decreases). Herein, asan indicator indicating the exchange coupling force, Hn/Hc is used.Actually, the value of the gradient a of magnetization curve ispreferably, but Hn can be seen easier than the value of the gradient a,and the value of Hn is used to examine.

In magnetic recording media where on the glass substrate weresuccessively layered a soft magnetic layer (CoTaZrFe/Ru/CoTaZrFe) with athickness of 60 nm, orientation control layer (NiW) with a thickens of10 nm, underlayer (Ru) with a thickness of 20 nm, magnetic recordinglayer (CoCrPt-oxide) with a thickness of 13 nm, exchange coupling layer,medium protective layer with a thickness of 5 nm, and lubricating layerwith a thickness of 1.3 nm, Hc and Hn were obtained when the filmthickness of the exchange coupling layer 24 was 10. 5 nm, 7 nm, 5.5 nm,4 nm and 0 nm. In addition, Hc and Hn were measured using NEOARKcorporation Kerr magnetism measurement equipment, while applying theexternal magnetization with the Kerr diffraction angle of the magneticrecording layer set at the perpendicular direction. The results areshown in FIG. 4. As can be seen from FIG. 4, as the exchange couplingincreases (the thickness of the exchange coupling layer decreases), therectangular shape of hysteresis of the magnetization curve is better,and the absolute value of Hn increases.

Further, the gradient a of the magnetization curve and the value ofHn/Hc were obtained when the film thickness of the exchange couplinglayer 24 was thus 10. 5 nm, 7 nm, 5.5 nm, 4 nm and 0 nm. The results areshown in FIG. 5. As can be seen from FIG. 5, in the gradient a of themagnetization curve, equal values are obtained in no exchange couplinglayer 24 and the exchange coupling layer with a thickness of 5.5 nm.Meanwhile, the value of Hn/Hc is higher as the film thickness of theexchange coupling layer 24 is thinner. Thus, with respect to theexchange coupling force in the exchange coupling layer when the filmthickness is changed, it is understood that using Hn/Hc as an indicatoris preferable to using a as an indicator.

Then, in the magnetic recording media with the above-mentionedconfiguration, the inventors of the invention examined Hn/Hc when ionirradiation was performed on the exchange coupling layer while changingthe film thickness of the exchange coupling layer 24 to 10.5 nm, 7 nmand 5.5 nm. The results are shown in FIG. 6. As can be seen from FIG. 6,with respect to Hn/Hc to be an indicator of the exchange coupling force,almost the same values are shown in the exchange coupling layer with athickness of 10.5 nm without undergoing ion irradiation and the exchangecoupling layer with a thickness of 7 nm with ion irradiation (dose:4×10¹³ (ions/cm²) performed thereon. In other words, by performing ionirradiation on the exchange coupling layer, although the film thicknesswas thin, it was possible to cause the high exchange coupling force tobe exerted.

In the invention, Hn/Hc is a negative value, preferably −0.2 or less,and more preferably, −0.5 or less. Further, in this range, it ispreferable that a value is lower in the case of performing ionirradiation than in the case of not performing ion irradiation, and itis more preferable that a value is lower in the case of performing ionirradiation than in the case of not performing ion irradiation by −0.05or less. Accordingly, it is desirable to define the thickness of theexchange coupling layer so as to obtain such Hn/Hc, and further, it isdesirable to set conditions of ion irradiation so as to obtain such athickness of the exchange coupling layer. Furthermore, the reversedmagnetic domain nucleation magnetic field Hn is preferably −2000Oe(×10³/4π A/m) or more.

The magnetic recording media with the above-mentioned configurationexhibit the high exchange coupling force by performing ion irradiationon the exchange coupling layer, although the film thickness is thin.Therefore, without increasing the spacing loss, it is possible to obtainexcellent magnetic recording reproduction characteristics with theexchange coupling force exerted. Further, in the method of theinvention, by ion irradiation, it is possible to effectively controlminute exchange coupling occurring between the magnetic recording layerhaving a fine structure hard to prepare and the exchange coupling layer,it is thus possible to perform with ease without changing variouscharacteristics as a magnetic recording medium, and the magneticrecording media can thereby be manufactured without reducingproductivity.

Further, the magnetic recording medium according to the invention is amagnetic recording medium provided with a magnetic recording layerhaving a granular structure with nonmagnetic layers between magneticparticles, and an exchange coupling layer that is provided on themagnetic recording layer to subject the magnetic particles to exchangecoupling, and may have a configuration that the exchange coupling layercontains a metal having a hexagonal close-packed structure, and anamount of change in the ratio c/a of the c axis to the a axis in acrystal lattice of the metal ranges from 10.21% to 10.81%.

Furthermore, in the magnetic recording medium according to theinvention, such a structure is more preferable that the exchangecoupling layer is a film containing Pt and Co, and that the metal is Co.

Still furthermore, in the magnetic recording medium according to theinvention, such a structure is more preferable that the thickness of theexchange coupling layer ranges from 3 nm to 7 nm.

Moreover, in the magnetic recording medium according to the invention,such a structure is more preferable that the ratio Hn/Hc of reversedmagnetic domain nucleation magnetic field Hn to coercive force Hc is−0.2 or less in the exchange coupling layer.

Further, a method of manufacturing a magnetic recording medium of theinvention is a method of manufacturing a magnetic recording mediumprovided with a magnetic recording layer having a granular structurewith nonmagnetic portions between magnetic particles, and an exchangecoupling layer provided on the magnetic recording layer to add an actionof exchange coupling the magnetic particles, where the method may have aconfiguration that ion irradiation is performed on the exchange couplinglayer, and that an amount of change in the ratio c/a of the c axis tothe a axis in a crystal lattice of a metal having a hexagonalclose-packed structure contained in the exchange coupling layer is10.21% or more.

Described next is an Example performed to clarify the effects of theinvention.

Example

Amorphous aluminosilicate glass was formed into a disk shape by directpress to prepare glass disks, and the glass disks were subjected tolapping, polishing and chemical strength successively to prepare theglass substrates. On the glass substrate were deposited successively asoft magnetic layer (CoTaZrFe/Ru/CoTaZrFe) with a thickness of 60 nm, aNiW film with a thickness of 10 nm, a Ru film with a thickness of 20 nm,a CorCrPt—SiO₂ film with a thickness of 13 nm, and an exchange couplinglayer (CoCrPt) with a thickness of 7 nm by a DC magnetron sputteringmethod in an atmosphere of Ar. Next, the exchange coupling layer wasirradiated with Ar⁺ ions with a dose of 4×10¹³ (ions/cm²). Then, acarbon layer with a thickness of 5 nm was formed on the exchangecoupling layer by a CVD method, a lubricating layer with a thickness of1.3 nm was formed on the carbon layer by a dip method, and magneticrecording media of this Example were prepared.

Electromagnetic conversion characteristic evaluations were performed onthe obtained magnetic recording media. The electromagnetic conversioncharacteristic evaluations were performed by examining recordingreproduction characteristics by a magnetic head using a spin stand. Morespecifically, signals were recorded while changing the recordingfrequency and further changing the recording density, reproductionoutputs of the signals were read, and the characteristics were thusexamined. In addition, as a magnetic head, a perpendicular recordingmerge type head was used where a perpendicular recording single-polehead (for recording) and GMR head (for reproduction) are merged. Theresults are shown in FIG. 7. FIG. 7 is a graph illustrating therecording density dependence of standardized output (normalized TAA)obtained from the output voltage.

Comparative Example

Magnetic recording media of a Comparative Example were prepared in thesame way as in the Example except ion irradiation being not performed onthe exchange coupling layer with a film thickness of the exchangecoupling layer of 10.5 nm. Electromagnetic conversion characteristicevaluations were performed on the obtained magnetic recording media inthe same way as in the Example. The results are also shown in FIG. 7.

As can be seen from FIG. 7, in the magnetic recording media of theExample, the so-called T₅₀ is improved that is the recording densitywhen an output voltage obtained from roll-off becomes 50%. In otherwords, in the magnetic recording media of this Example, the resolutionof a medium output is improved. This is because it is considered that inthe magnetic recording media of the Example, a desired exchange couplingforce is obtained by ion irradiation even when the film thickness isthin, and that the spacing loss is reduced.

The present invention is not limited to the above-mentioned Embodiment,and is capable of being carried into practice with modifications thereofas appropriate. For example, the magnetic recording layer and theexchange control layer are not limited particularly in their structures,but preferably, the magnetic recording layer is at least one magneticlayer having a granular structure, and as the exchange coupling layer,it is possible to use a layer having a granular structure, continuousfilm, the so-called cap layer where the degree of isolation of particlesis lower than that in the granular layer, or an amorphous layer withouthaving a crystal structure. Further, it is considered that the strongestexchange coupling is exerted when the magnetic recording layer and theexchange coupling are in direct contact with each other, but directcontact is not always necessary. Furthermore, as the relative positionsof the magnetic recording layer and the exchange coupling layer, it isconsidered better that the magnetic recording layer is arranged in thevicinity of a recording reproduction head, but in perpendicularrecording media and the like where a soft magnetic reinforcing layerexists to supplement the head write magnetic field, when the sufficientmagnetic field is applied to the recording layer, the exchange couplinglayer may be disposed closer to the head, and the magnetic layer may bedisposed relatively far from the head.

Moreover, the layer structures, the materials for members, the numbers,sizes, processing procedures and the like in the above-mentionedEmbodiment are of examples, and are capable of being carried intopractice with various modifications thereof within the scope ofexhibiting the effects of the invention. Further, the invention iscapable of being carried into practice with modifications thereof asappropriate without departing from the scope of the invention.

1. A magnetic recording medium comprising: a non-magnetic substrate; amagnetic recording layer of a granular structure, where pillar-shapedmagnetic particles spatially have nonmagnetic boundary portionstherebetween, on the nonmagnetic substrate; and an exchange couplinglayer provided on the magnetic recording layer to add an action ofexchange coupling the magnetic particles, wherein reversed magneticdomain nucleation magnetic field Hn is −2000Oe or more, a ratio Hn/Hc ofreversed magnetic domain nucleation magnetic field Hn to coercive forceHc is −0.5 or less, and a film thickness of the exchange coupling layeris 7 nm or less.
 2. The magnetic recording medium according to claim 1,wherein the exchange coupling layer contains Pt, Co and Cr.
 3. Themagnetic recording medium according to claim 1, wherein a thickness ofthe exchange coupling layer is nm or less
 4. The magnetic recordingmedium according to claim 1, wherein said exchange coupling layer beinga film containing a metal having a hexagonal closed packed structure andproviding an exchange coupling layer surface.
 5. The magnetic recordingmedium according to claim 1, wherein said exchange coupling layer hasbeen subject to ion irradiation.
 6. The magnetic recording mediumaccording to claim 5, wherein an amount of change in a ratio c/a of ac-axis to an a-axis in a crystal lattice of the metal having thehexagonal close-packed structure contained in the exchange couplinglayer is 10.21% or more after performing said ion irradiation.
 7. Themagnetic recording medium according to claim 1, wherein the exchangecoupling layer is a film containing Pt and Co, and the metal is Co. 8.The magnetic recording medium according to claim 1, wherein and aprotective layer is on the exchange coupling layer.
 9. The magneticrecording medium according to claim 5 wherein a dose in the ionirradiation is in the range of 1×10¹³ to 1×10¹⁵ (ions/cm²).